A variety of imaging techniques are available for imaging different anatomical structures of the body, such as X-ray imaging, typically used for imaging bones, Computer Tomography (CT), typically used for generating a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation, Magnetic Resonance Imaging (MRI), or Nuclear Magnetic Resonance Imaging (NMRI), used most commonly to visualize the internal structure and function of the body, including soft tissues as well as bones, Diagnostic sonography (ultrasound scanning), used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions and Positron Emission Tomography (PET), where a three-dimensional image or picture of functional processes in the body is produced by creating images of the passage of a radioactive tracer through the body.
It is often desirable to register images produced by such modalities, for example for full spine imaging, and there is an emerging trend to register images produced by different techniques to each other. To do this, reference points are required to register the various images. Different skin markers are available to suit each imaging technique. However, these markers are all different and may not be transferable between modalities, meaning that they need to be removed and alternative ones replaced between different scanning operations, leading to a risk of placement error and mis-registration of the various images produced.
Many markers also have difficulty in attaching to the skin, due to hair and moisture, and some have very small surface areas, increasing this problem. Furthermore, none of the known markers are suitable for reliable recognition by 3D surface scanning technologies, which are increasingly used in volumetric analysis and surface profiling/measurement operations.